Appendix F Detailed Cover Type Tables - USDA Rural Development

Bemidji – Grand Rapids
Biological Assessment and Evaluation
Species Description
The Conservation Assessment for Black‐throated Blue Warbler (Dendroica caerulescens) (Burdett &
Niemi 2003) includes the following species description:
Although both sexes weigh about 10 g and share a relatively stocky, short‐necked
appearance, the male and female of this species bear little resemblance to each other.
In fact, in the early‐ and mid‐19th century the male and female Black‐throated Blue
Warbler were believed to be separate species with the female mistakenly classified as
the Pine Swamp Warbler (Audubon 1841). The species does not molt into a vastly
different fall plumage so year‐round identification is simplified. The male is a distinctive
dark rich blue above with black on the throat, sides of the head, and sides of the breast.
Some feathers on the dark blue back show central black spotting. The underside of the
male is snowy white (including axillars and underwing coverts) with an occasional slight
buff or yellow on the flanks. Remiges and rectices are black with subterminal white
spots on the outer rectices. The primary and secondary coverts are black. There is a
distinctive white spot at the base of the primaries that extends 9‐14 mm beyond the
greater primary coverts (Holmes 1994). Younger males can be distinguished from after
second year males by the dull primary coverts, olive green margins on most feathers but
particularly the alula coverts, ashy gray edgings to the various black regions, brown tint
to primaries and secondaries, and bluish‐gray or bluish‐olive edging to remiges
(particularly secondaries and tertials) in younger males (Holmes 1994, Graves 1997a).
The female Black‐throated Blue Warbler lacks the distinctive blue, black, and white
coloration of the male. The female is olive green above with a buffy to yellowish
underside that becomes increasingly olive on the sides and flank. The tail is darker and
slightly grayer than the back. A distinctive whitish yellow supercillium occurs over the
eye. This streak continues into slight dark shading on the auriculars. The lower half of
the eye ring is white. Similar to the male, the female has a white spot at the base of the
primaries however it extends only 4‐8 mm beyond the greater primary coverts (Holmes
1994). Wing linings show a white tint. As females age the loss of feather edges makes
the dorsal surface take on a more olive and less green hue, and the ventral surface
becomes increasingly white and less yellow.
The southern subspecies D. c. cairnsi tends to be darker on the dorsal side of both males
and females (Holmes 1994). The dorsal blue on the back and crown of the male are
often marked with black patches. The female D. c. cairnsi is also a darker olive above
and on the flanks and has less yellow underside. Juveniles of both sexes and subspecies
are olive brown above with dark brown or black retrices and remiges. The retrices and
remiges of juvenile females tend to be browner with green edgings than the black with
blue edgings these areas display on juvenile males. On all juveniles the ventral surface is
a lighter olive than the dorsal region (Holmes 1994).
The vocalizations of this species are not as extensively studied as those of other
warblers. Holmes (1994) provides an excellent summary of the vocalizations of D.
caerulescens.
Despite scattered documentations of female singing, almost all singing is performed by
males. Singing occurs almost exclusively during the breeding season from early May
through early August. At least three distinct songs have been recognized in this warbler.
The first is the most commonly heard song, typically referred to as a buzzy zee‐zee‐zee‐
July 2010 Species and Associated Habitat Page 4‐15